Beloved polar bear Knut has died

A Berlin zoo official says world-famous polar bear Knut has died.

Bear keeper Heiner Kloes said that four-year-old Knut died Saturday afternoon while alone in his compound. He says the cause is not yet clear.

Kloes says a post mortem will be conducted on Monday to try to pinpoint his cause of death.

Knut rose to stardom when he was hand-raised by zoo keepers after his mother rejected him at birth.

At one time the subject of international controversy after a human rights activist said that Knut should have been killed rather than humiliated by being raised "as a domestic pet". He declared that the zoo was violating animal protection legislation by keeping him alive

Knut became the center of a mass media phenomenon dubbed "Knutmania" that spanned the globe and spawned toys, media specials, DVDs, and books. Because of this, the cub was largely responsible for a significant increase in revenue, estimated at about five million euros, at the Berlin Zoo in 2007.